Bootstrapping an app for both Joomla 2.5 and Joomla 3.3

import.php

<?php
// Set flag that this is a parent file.
// We are a valid Joomla entry point.
define('_JEXEC', 1);

// Setup the base path related constants.
define('JPATH_BASE', dirname(dirname(dirname(dirname(dirname(__FILE__))))));
define('JPATH_COMPONENT_ADMINISTRATOR', dirname(dirname(__FILE__)));
define('JPATH_PLATFORM', JPATH_BASE . '/libraries');

// Bootstrap the application.
require_once JPATH_BASE . '/includes/defines.php';
require_once JPATH_PLATFORM . '/import.php';

// Register PHP namespaces if we are on Joomla 3
if (file_exists(JPATH_PLATFORM . '/classmap.php'))
{
	JLoader::registerNamespace('Joomla', JPATH_PLATFORM . '/framework');
	require_once JPATH_PLATFORM . '/classmap.php';
}

// Import the JApplicationWeb class from the platform.
jimport('joomla.application.web');

/**
 * The import class.
 */
class Import extends JApplicationWeb
{
  /**
	 * Execute the import.
	 *
	 * @return  void.
	 */
	protected function doExecute()
	{
	  // Put code here
	}
}

JApplicationWeb::getInstance('Import')->execute();